Second-generation biofuels, which are derived from biomass, have attracted worldwide attentions as a renewable energy source. Suitable feed stocks for the first-generation biofuels production are corn, wheat, sugarcane, soybean, grapes, seed and sunflowers. A major problem with these feed stocks is that they are also used for food and feed production and resource/land allocation is competitive with food production. To circumvent a conflict between demand for biofuel and food sources, cellulose-containing food waste and wood chips have been used as substrates for the second-generation biofuels. Breakdown of cellulose to sugar molecules is a required step before the fermentation process for ethanol production. However, a drawback in the development of this technology is that industrial-scale hydrolysis of cellulose is an expensive process due in large part to the cost of cellulases, the enzymes that degrade cellulose.
Cellulose is contained in nearly every natural, free-growing plant, tree, and bush, in meadows, forests, and fields all over the world without agricultural effort or cost needed to make it grow. One of the benefits of cellulosic ethanol is it reduces greenhouse gas emissions (GHG) by 85% over reformulated gasoline. By contrast, starch ethanol (e.g., from corn), which most frequently uses natural gas to provide energy for the process, may not reduce GHG emissions at all depending on how the starch-based feedstock is produced. According to the National Academy of Sciences as of 2011, there is no commercially feasible bio-refinery in existence capable of cost-effectively converting cellulosic biomass to fuel.
Ethanol is produced mostly from sugars or starches obtained from fruits and grains. In contrast, cellulosic ethanol is obtained from cellulose, the main component of wood, straw, and much of the structure of plants. Since cellulose cannot be digested by humans, the production of cellulose does not compete with the production of food. Moreover, since cellulose is the main component of plants, the whole plant can be harvested. This results in much better yields-up to 10 short tons per acre (22 t/ha), instead of 4-5 short tons/acre (9-11 t/ha) for the best crops of grain.
An estimated 323 million tons of cellulose-containing raw materials which could be used to create ethanol are thrown away each year in US alone. Furthermore, even land considered marginal for agricultural use could be planted with cellulose-producing crops, such as switchgrass, conceivably resulting in enough production to substitute for all the current oil imports into the United States.
Clearly there is a critical need in the art for more efficient methods for producing cellulases from cellulosic biomass for the cost-effective mass production of second-generation biofuels.